In wireless communication systems, a plurality of users can share the same radio resource through non-orthogonally multiplexing. For convenience, the plurality of users using the same radio resource through non-orthogonally multiplexing is called users within a same user group. Currently, in wireless communication systems, different users within a user group can be assigned different power allocation coefficients so as to distinguish each user. Further, a user within the user group can receive data of its own through an interference cancellation process. In order to conduct interference cancellation, in addition to its own control information, e.g., signaling or information that assists data transmission, such as resource allocation information, channel coding rate, modulation and coding scheme, the user needs to know control information of users in previous interference cancellation stages. Therefore, the issue of how to transmit control information of users in a wireless communication system is to be addressed in the existing wireless communication systems.